Image forming apparatus for embedding error detection information within a scanned image

ABSTRACT

An image forming apparatus includes an image forming unit, an image reading unit, an image inspecting unit and a history generating unit. The image forming unit forms an image on a sheet. The image reading unit reads a sheet face on which the image is formed, thereby generating a scan image. The image inspecting unit compares the generated scan image with a normal image to detect an error in the scan image. When the image inspecting unit detects the error, the history generating unit generates detection information on the detected error and embeds the generated detection information in the scan image, thereby generating a history image.

FIELD OF THE INVENTION

The present invention relates to an image forming apparatus and ahistory generating method.

DESCRIPTION OF THE RELATED ART

Conventionally, after forms an image on a sheet, an image formingapparatus compares a scan image obtained by reading the sheet face onwhich the image is formed with its normal image, which has beeninspected, to detect errors such as stains, color shift errors, positionshift errors and the like.

When an error is detected, a difference between the scan image and thenormal image is displayed, whereby a user can confirm the image regionwhere the error is detected. (Refer to, for example, Japanese PatentApplication Publication No. 2000-29198.)

However, in order to perform such display, a dedicated application whichcan calculate the difference between the scan image and the normal imageis required, and hence user-friendliness is low.

As to text (character) images, by utilizing an art of embedding PDFtexts, a general application for creation of and reference to PDF filescan be used to place and display a normal text image on a read textimage. (Refer to, for example, Japanese Patent Application PublicationNos. 2009-288974, 2004-280514 and 2011-150599.)

However, images formed by an image forming apparatus are not limited totext images but include, for example, graphics images and pictureimages. However, there have been no measures to provide detectioninformation on errors detected in text images as well as in the otherimages, the detection information indicating positions, sizes, types,levels and the like of the detected errors, in an easily confirmableform by use of a general application.

BRIEF SUMMARY OF THE INVENTION

Objects of the present invention include providing a history image whichmakes it easy to confirm error detection information.

In order to achieve at least one of the above objects, according to anaspect of the present invention, there is provided An image formingapparatus including: an image forming unit which forms an image on asheet; an image reading unit which reads a sheet face on which the imageis formed, thereby generating a scan image; an image inspecting unitwhich compares the generated scan image with a normal image to detect anerror in the scan image; and a history generating unit which, when theimage inspecting unit detects the error, generates detection informationon the detected error and embeds the generated detection information inthe scan image, thereby generating a history image.

Preferably, in the image forming apparatus, the history generating unitgenerates an error name text of a name of the error as the detectioninformation and embeds the generated error name text in one or morerectangular regions containing an error-detected image region, where theerror is detected.

Preferably, in the image forming apparatus, the name is composed of oneof or any combination of (i) a type, (ii) an identification number and(iii) a level of the error.

Preferably, in the image forming apparatus, the history generating unitdetermines one rectangular region circumscribing the error-detectedimage region as a text embedment region, where the error name text is tobe embedded, and determines a format and a layout of the error name textsuch that a size of the text embedment region agrees with a size of theerror name text when embedded in the text embedment region.

Preferably, in the image forming apparatus, the history generating unitdetermines one or more rectangular regions placed over theerror-detected image region as one or more text embedment regions, wherethe error name text is to be embedded, and determines a format and alayout of the error name text such that a size or sizes of the one ormore text embedment regions agrees with a size of the error name textwhen embedded in the one or more text embedment regions.

Preferably, in the image forming apparatus, the error name text has atransparent color.

Preferably, in the image forming apparatus, the history generating unitgenerates a bookmark using the error name text and embeds the generatedbookmark in the scan image.

Preferably, in the image forming apparatus, the history generating unitgenerates an image clearly showing an error-detected image region, wherethe error is detected, as the detection information and embeds thegenerated image in the scan image as a layer different from a layer ofthe scan image.

Preferably, in the image forming apparatus, the history generating unitgenerates, as the image clearly showing the error-detected image region,at least one of (i) an image accentuating the error-detected imageregion and (ii) an image of the error-detected image region placed onthe normal image.

Preferably, in the image forming apparatus, the image inspecting unitdetects the error of at least one type among an image defect, a colorshift and a position shift.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The present invention is fully understood from the detailed descriptiongiven hereinafter and the accompanying drawings, which are given bywayof illustration only and thus are not intended to limit the presentinvention, wherein:

FIG. 1 is a front view showing the configuration of an image formingapparatus according to an embodiment of the present invention;

FIG. 2 is a block diagram showing, by function, components of the imageforming apparatus shown in FIG. 1;

FIG. 3 is a flowchart showing a procedure taken by the image formingapparatus to generate a history image(s);

FIG. 4A shows one rectangular region circumscribing an error-detectedimage region, where an error is detected;

FIG. 4B shows four rectangular regions having the same size and placedover the error-detected image region;

FIG. 5A shows an example of an error name text composed of characters invertical writing;

FIG. 5B shows an example of the error name text with the angle of thecharacters adjusted;

FIG. 5C shows an example of the error name text with the angle andaspect ratio of the characters adjusted;

FIG. 6A shows an example of a normal image;

FIG. 6B shows an example of a scan image where an error name text isembedded;

FIG. 6C shows an example of the normal image where an image clearlyshowing an error-detected image region is embedded;

FIG. 7 shows an example of a color chart where an error name text(s) isembedded;

FIG. 8 shows examples of register marks where error name texts andimages clearly showing error-detected image regions are embedded;

FIG. 9 shows an example of a display screen displaying a bookmark;

FIG. 10A shows an example of a display screen displaying a normal image;

FIG. 10B shows an example of the display screen displaying the normalimage with an error-detected image region placed;

FIG. 10C shows an example of the display screen displaying a scan imagewith an image accentuating the error-detected image region placed; and

FIG. 10D shows an example of the display screen displaying an error nametext embedded by note annotation.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of an image forming apparatus and a historygenerating method of the preset invention is described, referring to thedrawings.

FIG. 1 schematically shows the configuration of an image formingapparatus 1 according to an embodiment of the present invention.

As shown in FIG. 1, the image forming apparatus 1 includes an imageforming unit 18 and forms with the image forming unit 18 images based onbitmap initial images on sheets of paper with color materials such astoners.

The image forming apparatus 1 also includes an image reading unit 19 ona paper conveyance path on the downstream side of the image forming unit18. The image forming apparatus 1 reads with the image reading unit 19sheet faces on which images are formed, thereby generating scan images,and carries out inspection to detect errors, such as stains, color shifterrors and the like, in the generated scan images.

FIG. 2 shows, by function, components of the image forming apparatus 1.

As shown in FIG. 2, the image forming apparatus 1 includes a controlunit 11, a storage unit 12, an operation unit 13, a display unit 14, acommunication unit 15, an image generating unit 16, an image processingunit 17, an image forming unit 18 (described above), an image readingunit 19 (described above), an image inspecting unit 20 and a historygenerating unit 21.

The control unit 11 reads programs stored in the storage unit 12 andexecutes the programs, thereby controlling the units and the like of theimage forming apparatus 1. The control unit 11 includes a CPU (CentralProcessing Unit) and a RAM (Random Access Memory).

The control unit 11 allows the image processing unit 17 to process (i.e.to perform image processing on) the initial images generated by theimage generating unit 16 and allows the image forming unit 18 to formimages based on the processed initial images on sheets of paper, forexample.

The control unit 11 also allows the image forming unit 18 to form animage for color shift error detection and an image for position shifterror detection, which are respectively for calibration and correctionof position shift errors. As to initial images of these, the controlunit 11 may generate the initial images or may read the initial imageswhich are generated in advance and stored in the storage unit 12.

The storage unit 12 stores therein programs readable by the control unit11, data used for execution of the programs and the like. As the storageunit 12, a mass memory such as a hard disk can be used.

The storage unit 12 also stores therein scan images generated by theimage reading unit 19, images for histories (history images) generatedby the history generating unit 21 and the like.

The operation unit 13 and the display unit 14 are, as shown in FIG. 1,disposed at the upper part of the image forming apparatus 1 as a userinterface.

The operation unit 13 generates operation signals corresponding to useroperations and outputs the signals to the control unit 11. As theoperation unit 13, keys or a touchscreen integrated with the displayunit 14 can be used, for example.

The display unit 14 displays an operation screen and the like, followinginstructions from the control unit 11. As the display unit 14, an LCD(Liquid Crystal Display), an OELD (Organic Electro Luminescence Display)or the like can be used.

The communication unit 15 communicates with external apparatuses on anetwork, such as a user terminal, a server and another image formingapparatus (i.e. an image forming apparatus other than the image formingapparatus 1).

The communication unit 15 receives data (PDL data) described in a pagedescription language (PDL) from a user terminal via the network, forexample. The communication unit 15 can send history images to externalapparatuses via the network.

The image generating unit 16 generates bitmap initial images by color,namely, C (cyan), M (magenta), Y (yellow) and K (black), by rasterizingthe PDL data received by the communication unit 15. The pixels of eachinitial image have their respective gradation values. The gradationvalues are data values representing tone of the image. For example,8-bit data values represent the tone in 0 to 255 gradations,respectively.

The image generating unit 16 can also generate the initial images byreading with an image reading unit 161 images on documents set by users.The image reading unit 161 is disposed at the upper part of the imageforming apparatus 1 as shown in FIG. 1.

The image processing unit 17 performs image processing which isexemplified by gradation processing and halftone processing on theinitial images generated by the image generating unit 16.

The gradation processing is processing to convert (correct) gradationvalues of pixels of an initial image into gradation values with whichdensity characteristics of an image formed on a sheet match targetdensity characteristics.

The halftone processing is exemplified by error diffusion and screeningemploying ordered dithering.

The image forming unit 18 forms an image composed of multiple colors (C,M, Y and K) on a sheet according to gradation values of pixels of theinitial images processed by the image processing unit 17.

The image forming unit 18 includes, as shown in FIG. 1, four writingunits 181, an intermediate transfer belt 182, a pair of secondarytransfer rollers 183, a fixing device 184, paper feed trays 185 and areversal mechanism 186. The writing units 181 are disposed in seriesalong the belt surface of the intermediate transfer belt 182. Theintermediate transfer belt 182 rotates by being wounded around aplurality of rollers. One of the rollers is one of the secondarytransfer rollers 183. The secondary transfer rollers 183 and the fixingdevice 184 are disposed on the paper conveyance path for paper carriedfrom the paper feed trays 185. The paper feed trays 185 each housesheets of paper.

The four writing units 181 form C, M, Y and K images, respectively. Thewriting units 181 are the same in configuration, and each of themincludes an exposure unit 18 a, a photoreceptor 18 b, a developing unit18 c, a charger 18 d and a cleaner 18 e.

In each writing unit 181, the charger 18 d applies a voltage to thephotoreceptor 18 b, thereby charging the photoreceptor 18 b, theexposure unit 18 a irradiates the photoreceptor 18 b with laser beamsaccording to gradation values of pixels of a C, M, Y or K image, therebyexposing the photoreceptor 18 b, and then the developing unit 18 csupplies a color (C, M, Y or K) material such as a toner to develop anelectrostatic latent image formed on the photoreceptor 18 b, therebyforming the C, M, Y or K image on the photoreceptor 18 b.

The C, M, Y and K images formed on the respective photoreceptors 18 bare successively transferred onto the intermediate transfer belt 182 insuch a way as to be superimposed on top of each other, whereby an imagecomposed of multiple colors (C, M, Y and K) is formed on theintermediate transfer belt 182. After the C, M, Y and K images aretransferred thereonto, the cleaners 18 e of the writing units 181 removethe color materials remaining on the respective photoreceptors 18 b.

When a sheet is supplied from any one of the paper feed trays 185 andthe image composed of the multiple colors on the intermediate transferbelt 182 is transferred onto the sheet by the secondary transfer rollers183, the fixing device 184 heats and presses the sheet, thereby fixingthe image to the sheet. In the case where the image is formed on bothsides of the sheet, the sheet is reversed by the reversal mechanism 186and carried to the secondary transfer rollers 183 again.

As shown in FIG. 1, the image reading unit 19 is a line sensor, an areasensor or the like disposed on the paper conveyance path. The imagereading unit 19 reads the sheet face having the image formed by theimage forming unit 18, thereby generating a bitmap scan image.

The scan image generated by the image reading unit 19 is transferred tothe storage unit 12 via an image transfer path employing an interfacesuch as PCI express.

The image inspecting unit 20 compares the scan image generated by theimage reading unit 19 with its normal image to detect errors in the scanimage. As the normal image, usable are the initial images and a scanimage of a sheet determined as having no errors by a user who inspects aplurality of sheets on which the image is formed.

Types of errors detectable by the image inspecting unit 20 include animage defect (“defect” hereinafter), a color shift and a position shift.The image inspecting unit 20 detects errors of at least one type amongthese types.

For defect error detection, the image inspecting unit 20 compares a scanimage with its normal image and detects a defect error(s), such asstreaks, wrinkles, stains, image errata and image disappearances, in thescan image. For example, the image inspecting unit 20 determines afeature point of a scan image and its normal image, calculates a featureamount of the feature point, determines whether or not the scan imageand the normal image are similar to each other based on the featureamount with a discriminant analysis method, and when determines that thescan image and the normal image are dissimilar from each other based onthe feature amount, detects the feature point in the scan image as animage region where a defect error occurs (i.e. an error-detected imageregion).

For color shift error detection, the image inspecting unit 20 compares ascan image with its normal image and detects an image region(s) in thescan image, the image region being different in gradation value from itscorresponding image region in the normal image, as an image region wherea color shift error occurs (i.e. an error-detected image region). Theimage inspecting unit 20 calculates a difference between a gradationvalue of a scan image and a gradation value, which serves as a referencevalue, of its normal image as a color shift amount. In the case where animage for color shift error detection is formed for calibration, theimage inspecting unit 20 may detect a color shift error(s) in a scanimage of this image. The image for color shift error detection to use isexemplified by an image of a color chart composed of patches havingdifferent gradation values of the primary colors (C, M, Y and K), thesecondary colors (mixed colors of the primary colors) and the like.

For position shift error detection, the image inspecting unit 20compares a scan image with its normal image and detects an imageregion(s) in the scan image, the image region being different inposition from its corresponding image region in the normal image, as animage region where a position shift error occurs (i.e. an error-detectedimage region). In the case where an image for position shift errordetection is formed for correction of position shift errors, the imageinspecting unit 20 may detect a position shift error(s) in a scan imageof this image. The image for color shift error detection to use isexemplified by an image of a cross called the register mark. The imageinspecting unit 20 compares the image for color shift error detection ina scan image with that in its normal image in terms of position anddetects the image region of the image in the scan image as an imageregion where a position shift error occurs when the image in the scanimage and the image in the normal image are different from each other inposition. More specifically, the image inspecting unit 20 compares, forexample, an image of a register mark in a scan image with that in itsnormal image in terms of distance from the edge of a sheet to the imageof the register mark and detects the image region of the register markin the scan image as an image region where a position shift error occurswhen the image in the scan image and the image in the normal image aredifferent from each other in the distance. The image inspecting unit 20calculates a difference between the position of the image for positionshift error detection in the scan image and the position thereof in thenormal image as a position shift amount.

The history generating unit 21 generates a history image using the scanimage generated by the image reading unit 19. The history image isevidence that image formation has been performed and can be utilized forinspection, confirmation and the like of a printed matter obtained bythe image formation.

When the image inspecting unit 20 detects an error, the historygenerating unit 21 generates detection information on the detected errorand embeds the generated detection information in the scan mage, therebygenerating a history image. The history generating unit 21 stores thegenerated history image in the storage unit 12, but may store thehistory image in an external apparatus on a network through thecommunication unit 15.

The image inspecting unit 20 and the history generating unit 21 may becomposed of hardware resources such as LSIs (Large Scale Integrations).Software processing by a computer such as a CPU reading and executing aprogram(s) for image inspection and history image generation can realizethe same processing content as the hardware resources.

FIG. 3 shows a procedure taken by the image forming apparatus 1 togenerate a history image(s).

As shown in FIG. 3, in the image forming apparatus 1, the image formingunit 18 forms an image of one page on a sheet (Step S1).

The image reading unit 19 reads the sheet face on which the image isformed, thereby generating a scan image (Step S2). The image inspectingunit 20 compares the scan image generated by the image reading unit 19with its normal image to detect errors in the scan image (Step S3).

The history generating unit 21 converts the file format of the scanimage generated by the image reading unit 19 from the bitmap format toPDF (Step S4). If the image inspecting unit 20 detects no errors (StepS5; NO, Step S8; NO, and Step S11; NO), a history image of one page isobtained through the conversion of the file format to PDF.

On the other hand, if the image inspecting unit 20 detects a defecterror (Step S5; YES), the history generating unit 21 generates an errorname text for the defect error as detection information on the defecterror. The history generating unit embeds the generated error name textin one or more rectangular regions containing the error-detected imageregion, where the defect error is detected in the scan image (Step S6).

Because the file format is PDF, tools of note annotation and textannotation prepared in an application for creation of PDF files can beutilized to embed the error name text. The note annotation is a tool toadd a text to any region on a page, whereas the text annotation is atool to add emending instructions to replace a text with another, add atext, change paragraphs on a page and the like.

The name of an error (i.e. an error name) is preferably composed of oneof or any combination of (i) a type, (ii) an identification number and(iii) a level of the error, so that retrieval of the error name text(i.e. the error) can be easy.

The identification number is, for example, a page number indicating apage where the error is detected and/or a detection number indicatingwhat number the error is in order of detected errors in the page. Thelevel is, for example, the color shift amount or the position shiftamount calculated by the image inspecting unit 20.

It is further preferable that the type, identification number and/orlevel be combined with a piece(s) of information with which a printedmatter as an inspection target is identifiable, such as a serial numberof an image forming apparatus which has formed the image, the name of ajob for the image formation and a file name of the initial images, sothat retrieval of the error can be easier.

For example, the defect error name text “JobA_p4err001” is generated bycombining the text “JobA” indicating that the job name is A, the text“p4” indicating that the error-detected page is page 4, the text “err”indicating that the error type is the defect, and the text “001”indicating that the error is the first detected in the page.

The history generating unit 21 can determine one rectangular regioncircumscribing the error-detected image region, where the defect erroris detected, as a text embedment region, where the error name text is tobe embedded, and determine the format and layout of the error name textsuch that the size of the text embedment region agrees with the size ofthe error name text when embedded in the text embedment region.

FIG. 4A shows, as a text embedment region, one rectangular region g2circumscribing an image region g1 where an oblique line-shaped stain isdetected.

In this case, the start point P0 of the rectangular region g2 can bedetermined as the position of the text embedment region, and the widthdx1 in the main scanning direction x and the width dy1 in the subscanning direction y of the rectangular region g2 can be determined asthe size of the text embedment region.

The format and layout of the error name text “JobAYp4err001” can bedetermined such that the size of the rectangular region g2 agrees withthe size of the error name text “JobAYp4err001” when embedded in therectangular region g2. Examples of the format include font size,character spacing and line spacing, and examples of the layout includethe number of rows in the rectangular region g2 and the number ofcharacters in a row in the rectangular region g2.

The history generating unit 21 can alternatively determine one or morerectangular regions placed over the error-detected image region, wherethe defect error is detected, as one or more text embedment regions anddetermine the format and layout of the error name text such that thesize or the sizes of the one or more text embedment regions agree withthe size of the error name text when embedded in the one or more textembedment regions.

FIG. 4B shows four rectangular regions g3 having the same size andplaced over the image region g1, where an oblique line-shaped stain isdetected, as text embedment regions.

In this case, the start points P1 to P4 of the respective rectangularregions g3 can be determined as the positions of the text embedmentregions, respectively, and the widths dx2 in the main scanning directionx and the widths dy2 in the sub scanning direction y of the respectiverectangular regions g3 can be determined as the sizes of the textembedment regions, respectively.

The format and layout of the error name text “JobAYp4err001” can bedetermined such that the sizes of the rectangular regions g3 agree withthe size of the error name text “JobAYp4err001” when embedded in therectangular regions g3. Examples of the format include font size,character spacing and line spacing, and examples of the layout includethe number of characters arranged in each rectangular region g3 and thenumber of rows in each rectangular region g3.

The history generating unit 21 can also adjust the arrangementdirection, angle, aspect ratio and the like of characters as the formatand layout of the error name text.

For example, FIG. 4A and FIG. 4B each show an example of charactersarranged from left to right, namely, in horizontal writing, but when atext embedment region is a vertically long and narrow rectangular, suchas a text embedment region g4 shown in FIG. 5A, the characters may bearranged from top to bottom, namely, in vertical writing, one by one.

FIG. 5B shows an example of the characters in vertical writing beingrotated 90°.

FIG. 5C shows an example of the characters shown in FIG. 5B beingarranged from left to right one by one with the aspect ratio of thecharacters adjusted to agree with the size of the text embedment regiong4.

The error name text to embed preferably has a transparent color, so thateven if the error name text embedded in the scan image is displayed whenthe scan mage is displayed, the scan image is confirmable (i.e.seeable).

When embeds the error name text (Step S6), the history generating unit21 extracts, from the scan image, the error-detected image region, wherethe defect error is detected, and generates, as the detectioninformation on the defect error, an image clearly showing the extractederror-detected image region. As long as the image clearly shows theerror-detected image region, it may be an image clearly showing arectangular region(s) generated by extracting one or more rectangularregions containing the error-detected image region, like the textembedment region(s). The history generating unit 21 embeds the generatedimage in the scan image as a layer different from the layer of the scanimage (Step S7).

The image clearly showing the error-detected image region is at leastone of (i) an image accentuating the error-detected image region,thereby being more noticeable than the other region, by hatching,brightness inversion or the like and (ii) an image of the error-detectedimage region placed on the normal image at a position corresponding tothe position of the error-detected image region in the scan image.Either of the images makes it easy to grasp the error-detected imageregion.

In the case of the above (ii) image, namely, the image of theerror-detected image region placed on the normal image, if the normalimage and the image of the error-detected image region are embedded inthe scan image as different layers, this makes it easier to grasp theerror-detected image region because display switching of these imagesbecomes available.

FIG. 6A shows an example of a normal image. FIG. 6B shows an example ofa scan image where a stain (defect error) is detected and an error nametext thereof is embedded in one rectangular region g2 circumscribing anerror-detected image region g1, where the stain is detected.

FIG. 6C shows an example of an image clearly showing an error-detectedimage region. The image shown in FIG. 6C is an image generated by:extracting, as the error-detected image region, the rectangular regiong2, where the error name text is embedded, from the scan image shown inFIG. 6B; placing the rectangular region g2 on the normal image shown inFIG. 6A at a position corresponding to the position of the rectangularregion g2 in the scan image; and accentuating the rectangular region g2.

In the above, the procedure is described to embed detection informationon a defect error. However, the same procedure is used to embeddetection information on a color shift error and a position shift error.

If the image inspecting unit 20 detects a color shift error (Step S8),the history generating unit 21 generates an error name text for thecolor shift error. The history generating unit embeds the generatederror name text in one or more rectangular regions containing theerror-detected image region, where the color shift error is detected inthe scan image (Step S9), in the same way as the defect error.

Then, the history generating unit 21 generates an image clearly showingthe error-detected image region, where the color shift error isdetected, and embeds the generated image in the scan image as a layerdifferent from the layer of the scan image (Step S10).

FIG. 7 shows an example of a scan image of a color chart formed on asheet for color shift error detection. In the scan image, an error nametext(s) of color shift errors is embedded.

As shown in FIG. 7, the error name text(s) of the color shift errors isembedded in the image regions of patches where the color shift errorsoccur. The error name text(s) of the color shift errors is generated bycombining the text “dEerr” indicating that the error type is the colorshift and a text of a number indicating the color shift amount. Forexample, the error name text “dEerr002” indicates that a color shifterror is detected, and the color shift amount thereof is level 2.

If the image inspecting unit 20 detects a position shift error (StepS11; YES), the history generating unit 21 generates an error name textfor the position shift error. The history generating unit 21 embeds thegenerated error name text in one or more rectangular regions containingthe error-detected image region, where the position shift error isdetected in the scan image (Step S12), in the same way as the defecterror.

Then, the history generating unit 21 generates an image clearly showingthe error-detected image region, where the position shift error isdetected, and embeds the generated image in the scan image as a layerdifferent from the layer of the scan image (Step S13).

FIG. 8 shows examples of scan images of four register marks formed on asheet for position shift error detection. In the scan images, error nametexts of position shift errors are embedded.

As shown in FIG. 8, the error name texts of the position shift errorsare embedded in the image regions of, among four register marks, tworegister marks where the position shift errors occur. Each of the errorname texts of the position shift errors is generated by combining thetext “dXerr” indicating that the error type is the position shift in themain scanning direction x or “dYerr” indicating that the error type isthe position shift in the sub scanning direction y and a text of a signand a number indicating the position shift amount. For example, theerror name text “dXerr+1” in FIG. 8 indicates that the position of theregister mark in the scan image is shifted +1 mm to the end side in themain scanning direction x from the position of its correspondingregister mark in the normal image.

As shown in FIG. 8, as an image clearly showing the error-detected imageregion, where the color shift error is detected, an image accentuatingthe rectangular region circumscribing the register mark is embedded.

When the detection information on each of all the errors is embedded,the history generating unit 21 generates a bookmark using the error nametexts as indexes and embeds the generated bookmark in the scan image(Step S14). A history image of one page is obtained through theembedment of the bookmark.

In the bookmark, the error name texts can be described hierarchicallywith their error types, and also links to pages where the error nametexts are embedded can be described.

When no errors are detected, a bookmark indicating that the number ofdetected errors is 0 may be generated and embedded in the scan image.

After the history image of one page is generated, if history images ofall the pages have not been generated yet (Step S15; NO), the processreturns to Step S1 to generate a history image of the next page. On theother hand, if history images of all the pages have been generated (StepS15; YES), the history generating unit 21 combines the history images ofall the pages so as to store the history images as a history image ofone job in the storage unit 12 (Step S16).

The stored history image makes it easy to retrieve the errors detectedby the image inspecting unit 20 using the error name texts embedded inthe history image. The file format of the history image is PDF.Therefore, the errors can be easily retrieved by utilizing a generalapplication for reading PDF files, such as Acrobat®.

The bookmark embedded in the history image can be read and displayed,for example.

FIG. 9 shows an example of a display screen displaying the bookmark.

As shown in FIG. 9, the display screen is divided into left and rightsections. On the left section of the display screen, the bookmark isdisplayed. In the bookmark, the detected errors, such as color shifterrors and stains (defect errors), are displayed hierarchically withtheir error types, using their error name texts as indexes. On the rightsection of the display screen, the scan image of a page can bedisplayed, the page where an error name text selected from among theindexes is embedded.

This bookmark makes them possible to grasp the whole picture of theerror detection result and also to jump, of a plurality of pages, to apage where a specified error(s) is detected, and therefore makes it easyto confirm errors.

Further, the image clearly showing an error-detected image region, theimage being embedded in the history image, can be read and displayed. Ifboth the above (i) image, namely, the image accentuating anerror-detected image region, and the above (ii) image, namely, the imageof the error-detected image region placed on a normal image, areembedded as the image clearly showing the error-detected image region,display switching of (a) the normal image, (b) the image of theerror-detected image region placed on the normal image, (c) the scanimage, and (d) the scan image with the image of the error-detected imageregion placed becomes available.

FIG. 10A shows an example of a display screen displaying a normal image.FIG. 10B shows an example of the display screen displaying the normalimage with an error-detected image region placed. FIG. 10C shows anexample of the display screen displaying a scan image with an imageaccentuating the error-detected image region placed. Display switchingof these images makes it easy to confirm the white streak in the scanimage.

When an error name text is embedded by utilizing note annotation, asshown in FIG. 10D, (i) a balloon mark indicating that note annotation isutilized to embed the error name text and (ii) the error name text of,in this case, the streak can be displayed.

As described above, the image forming apparatus 1 includes: the imageforming unit 18 which forms an image on a sheet; the image reading unit19 which reads a sheet face on which the image is formed, therebygenerating a scan image; the image inspecting unit 20 which compares thegenerated scan image with a normal image to detect an error(s) in thescan image; and the history generating unit 21 which, when the imageinspecting unit detects the error(s), generates detection information onthe detected error and embeds the generated detection information in thescan image, thereby generating a history image.

By reading the detection information embedded in the history image, oneor more errors detected in the scan image can be easily retrieved.Further, an application supporting the file format which can embed andread texts and images can be utilized to embed and retrieve thedetection information. Thus, there is provided a history image whichmakes it easy to confirm error detection information without a dedicatedapplication to confirmation of the error detection result.

The above embodiment is a preferred example of the present invention.The present invention is not limited thereto and can be appropriatelymodified within the scope not departing from the spirit of the presentinvention.

In the above embodiment, a PDF history image is generated. However, thefile format of the history image is not limited to PDF and may be any aslong as it can embed and read texts and images. A file format using astructured language which adds meta-information (metadata) by tags canembed and read texts and images. Hence, for example, file formats suchas HTML and OOXML can also be utilized.

As a computer readable medium storing therein the program(s) to performthe procedure shown in FIG. 3, a nonvolatile memory such as a ROM or aflash memory or a portable storage medium such as a CD-ROM can be used.Further, as a medium to provide data of the program(s) via acommunication line, a carrier wave can be used.

This application is based upon and claims the benefit of priority under35 U.S.C. 119 of Japanese Patent Application No. 2015-021729 filed onFeb. 6, 2015, the entire disclosure of which, including thespecification, claims, drawings and abstract, is incorporated herein byreference in its entirety.

What is claimed is:
 1. An image forming apparatus comprising: an imageforming unit configured to form an image on a sheet, the image beingformed based on a target image; an image reading unit configured to reada sheet face on which the image is formed and generate a scan imagebased on the read sheet face; an image inspecting unit configured tocompare the scan image with the target image to detect an error in thescan image; and a generating unit configured to generate a modifiedimage by: (i) converting the scan image to one of Portable DocumentFormat (PDF), Hypertext Markup Language (HTML), and Office OpeneXtensible Markup Language (OOXML); and (ii) when the image inspectingunit detects the error, embedding error information regarding thedetected error in the scan image as a layer different from a layer ofthe scan image.
 2. The image forming apparatus according to claim 1,wherein the generating unit generates an error name text of a name ofthe error as the error information and embeds the generated error nametext in one or more rectangular regions containing an error-detectedimage region, where the error is detected.
 3. The image formingapparatus according to claim 2, wherein the name is composed of one ofor any combination of (i) a type, (ii) an identification number and(iii) a level of the error.
 4. The image forming apparatus according toclaim 2, wherein the generating unit determines one rectangular regioncircumscribing the error-detected image region as a text embedmentregion, where the error name text is to be embedded, and determines aformat and a layout of the error name text such that a size of the textembedment region agrees with a size of the error name text when embeddedin the text embedment region.
 5. The image forming apparatus accordingto claim 2, wherein the generating unit determines one or morerectangular regions placed over the error-detected image region as oneor more text embedment regions, where the error name text is to beembedded, and determines a format and a layout of the error name textsuch that a size or sizes of the one or more text embedment regionsagrees with a size of the error name text when embedded in the one ormore text embedment regions.
 6. The image forming apparatus according toclaim 2, wherein the error name text has a transparent color.
 7. Theimage forming apparatus according to claim 2, wherein the generatingunit generates a bookmark using the error name text and embeds thegenerated bookmark in the scan image.
 8. The image forming apparatusaccording to claim 1, wherein the generating unit generates an imageclearly showing an error-detected image region, where the error isdetected, as the error information.
 9. The image forming apparatusaccording to claim 8, wherein the generating unit generates, as theimage clearly showing the error-detected image region, at least one of(i) an image accentuating the error-detected image region and (ii) animage of the error-detected image region placed on the normal image. 10.The image forming apparatus according to claim 1, wherein the imageinspecting unit detects the error of at least one type among an imagedefect, a color shift and a position shift.
 11. The image formingapparatus according to claim 1, wherein the generating unit determinesone or more rectangular regions as one or more text embedment regions,where the error information is to be embedded, each of said one or morerectangular regions corresponding to a part of the whole scan image. 12.The image forming apparatus according to claim 1, wherein the generatingunit generates history images of a plurality of scanned images of a joband combines the history images of the plurality of scanned images ofthe job into a history image of the job.
 13. The image forming apparatusaccording to claim 12, wherein the generating unit generates a bookmarkusing the error information of the plurality of scanned images of thejob and embeds the bookmark in the history image of the job, thebookmark configured to hierarchically display and link the errorinformation to the plurality of scanned images such that selection ofparticular displayed error information causes the corresponding scannedimage to be displayed.
 14. A method comprising: forming an image on asheet based on a target image; reading a sheet face on which the imageis formed and generating a scan image based on the read sheet face;comparing the scan image with the target image to detect an error in thescan image; converting the scan image to one of Portable Document Format(PDF), Hypertext Markup Language (HTML), and Office Open eXtensibleMarkup Language (OOXML); and when the error is detected, embedding errorinformation regarding the detected error in the scan image as a layerdifferent from a layer of the scan image to generate a modified image.15. The method according to claim 14, further comprising determining oneor more rectangular regions as one or more text embedment regions, wherethe error information is to be embedded, each of said one or morerectangular regions corresponding to a part of the whole scan image. 16.The method according to claim 14, further comprising generating historyimages of a plurality of scanned images of a job and combining thehistory images of the plurality of scanned images of the job into ahistory image of the job.
 17. The method according to claim 16, whereinthe generating unit generates a bookmark using the error information ofthe plurality of scanned images of the job and embeds the bookmark inthe history image of the job, the bookmark configured to hierarchicallydisplay and link the error information to the plurality of scannedimages such that selection of particular displayed error informationcauses the corresponding scanned image to be displayed.
 18. An imageforming apparatus comprising: an image forming unit configured to forman image on a sheet, the image being formed based on a target image; animage reading unit configured to read a sheet face on which the image isformed and generate a scan image based on the read sheet face; an imageinspecting unit configured to compare the scan image with the targetimage to detect an error in the scan image; and a generating unitconfigured to generate a modified image by: (i) converting the scanimage to one of Portable Document Format (PDF), Hypertext MarkupLanguage (HTML), and Office Open eXtensible Markup Language (OOXML); and(ii) when the image inspecting unit detects the error, digitallyembedding error information regarding the detected error in the scanimage.
 19. The image forming apparatus according to claim 18, whereinthe error information is embedded in a PDF file, an HTML file, or anOOXML file corresponding to the scanned image.
 20. The image formingapparatus according to claim 18, wherein electronic data correspondingto the error information is embedded in the scan image.